U.S. patent application number 12/626137 was filed with the patent office on 2010-03-18 for method and apparatus for in-situ radiofrequency assisted gravity drainage of oil (ragd).
This patent application is currently assigned to KSN Energy LLC. Invention is credited to Raymond S. Kasevich.
Application Number | 20100065265 12/626137 |
Document ID | / |
Family ID | 40381072 |
Filed Date | 2010-03-18 |
United States Patent
Application |
20100065265 |
Kind Code |
A1 |
Kasevich; Raymond S. |
March 18, 2010 |
METHOD AND APPARATUS FOR IN-SITU RADIOFREQUENCY ASSISTED GRAVITY
DRAINAGE OF OIL (RAGD)
Abstract
The present invention relates generally to a radiofrequency
reactor for use in thermally recovering oil and related materials.
The radiofrequency reactor includes a radiofrequency antenna
configured to be positioned within a well, where the well is
provided within an area in which crude oil exists in the ground.
The radiofrequency antenna includes a cylindrically-shaped
radiating element for radiating radiofrequency energy into the area
in which crude oil exists. The cylindrically-shaped radiating
element is configured to allow passage of fluids there through. The
radiofrequency reactor also includes a radiofrequency generator
electrically coupled to the radiofrequency antenna. The
radiofrequency reactor is operable to control the radiofrequency
energy generated.
Inventors: |
Kasevich; Raymond S.; (Mount
Washington, MA) |
Correspondence
Address: |
OCCHIUTI ROHLICEK & TSAO, LLP
10 FAWCETT STREET
CAMBRIDGE
MA
02138
US
|
Assignee: |
KSN Energy LLC
Great Barrington
MA
|
Family ID: |
40381072 |
Appl. No.: |
12/626137 |
Filed: |
November 25, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12259828 |
Oct 28, 2008 |
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12626137 |
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11471276 |
Jun 20, 2006 |
7441597 |
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12259828 |
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60692112 |
Jun 20, 2005 |
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Current U.S.
Class: |
166/248 ;
166/57 |
Current CPC
Class: |
E21B 43/2401 20130101;
E21B 43/003 20130101; E21B 43/2408 20130101 |
Class at
Publication: |
166/248 ;
166/57 |
International
Class: |
E21B 43/24 20060101
E21B043/24; E21B 43/00 20060101 E21B043/00; E21B 36/00 20060101
E21B036/00 |
Claims
1. A radiofrequency reactor for use in thermally recovering oil and
related materials, the reactor comprising: a radiofrequency antenna
configured to be positioned within a well provided within an area
in which crude oil exists in the ground, the radiofrequency antenna
including a cylindrically-shaped radiating element for radiating
radiofrequency energy into the area in which crude oil exists, the
cylindrically-shaped radiating element configured to allow passage
of fluids there through; and a radiofrequency generator
electrically coupled to the radiofrequency antenna and operable to
control the radiofrequency energy generated.
2. The radiofrequency reactor of claim 1 wherein the
cylindrically-shaped radiating element includes a plurality of
apertures for allowing passage of the fluids.
3. The radiofrequency reactor of claim 2 wherein the plurality of
apertures have dimensions selected on the basis of the frequency of
the radiofrequency energy.
4. The radiofrequency reactor of claim 1 further comprising a
coaxial cable for coupling the radiofrequency antenna to the
radiofrequency generator.
5. The radiofrequency reactor of claim 1, further comprising a
choke assembly positioned between the radiofrequency antenna and
radiofrequency generator to maximize transmission of the
radiofrequency energy to the radiofrequency antenna.
6. The radiofrequency reactor of claim 5, wherein the choke
assembly includes an inner conductive casing surrounded by a
dielectric portion, the assembly running at least one-quarter of a
maximal frequency to be emitted, and the inner casing electrically
coupled to the radiofrequency generator and to the inside of the
well wall.
7. The radiofrequency reactor of claim 6, wherein the assembly runs
an odd-multiple of one-quarter of a maximal frequency to be
emitted.
8. The radiofrequency reactor of claim 1, wherein the reactor is
one in a plurality of reactors and the radiofrequency generator
operable to control the radiofrequency energy generated is
configured to work in conjunction with the radiofrequency
generators of the plurality.
9. The radiofrequency reactor of claim 1, wherein the
radiofrequency generator operable to control the radiofrequency
energy generated is configured to control the phase of the
radiofrequency energy emitted.
10. A method of retrofitting an oil well for extracting crude oil,
the method comprising: electrically coupling a radiofrequency
generator to a radiofrequency antenna including a
cylindrically-shaped radiating element for radiating radiofrequency
energy into the crude oil; and controlling the radiofrequency
generator to provide radiofrequency energy to the radiofrequency
antenna.
11. The method of claim 10, further comprising positioning the
radiofrequency generator proximally to the well surface and
electrically coupling the radiofrequency generator to the
cylindrically-shaped radiating element via a coaxial cable.
12. The method of claim 11, further comprising connecting a choke
assembly between the radiofrequency generator and the
cylindrically-shaped radiating element.
13. The method of claim 10, wherein controlling the radiofrequency
generator to provide radiofrequency energy to the radiofrequency
antenna comprises controlling the phasing of the radiofrequency
energy emitted.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority from U.S. provisional
patent application No. 60/692,112, which was filed on Jun. 20,
2005, and which is incorporated herein by reference in its
entirety. This application is a continuation-in-part application
of, and claims priority to, U.S. application Ser. No. 11/471,276,
filed Jun. 20, 2006, and now allowed, and which is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to the use of
radiofrequency energy to heat heavy crude oil or both heavy crude
oil and subsurface water in situ, thereby enhancing the recovery
and handling of such oil. The present invention further relates to
methods for applying radiofrequency energy to heavy oils in the
reservoir to promote in situ upgrading to facilitate recovery. This
invention also relates to systems to apply radiofrequency energy to
heavy oils in situ.
BACKGROUND OF THE INVENTION
[0003] Heavy crude oil presents problems in oil recovery and
production. Crude oils of low API gravity and crude oils having a
high pour point present production problems both in and out of the
reservoir. Extracting and refining such oils is difficult and
expensive. In particular, it is difficult to pump heavy crude oil
or move it via pipelines.
[0004] Recovery of heavy crude oils may be enhanced by heating the
oil in situ to reduce its viscosity and assist in its movement. The
most commonly used process today for enhanced oil recovery is steam
injection, where the steam condensation increases the oil
temperature and reduces its viscosity. Steam in the temperature
range of 150 to 300 degrees Fahrenheit may decrease the heavy oil
viscosity by several orders of magnitude. Cyclic steam simulation
(CCS) is a method that consists of injecting steam into a well for
a period of time and then returning the well to production. A
recently developed commercial process for heavy oil recovery is
steam assisted gravity drainage (SAGD), which finds its use in high
permeability reservoirs such as those encountered in the oil sands
of Western Canada. SAGD has resulted recovery of up to 65% of the
original oil in places, but requires water processing. All such
methods tend to be expensive and require the use of external water
sources.
[0005] Other methods in current use do not require the use of water
or steam. For example, processes such as the Vapex process, which
uses propane gas, and naphtha assisted gravity drainage (NAGD) use
solvents to assist in the recovery of heavy crude oils. The
drawback to these processes is that the solvents--propane or
naphtha--are high value products and must be fully recovered at the
end of the process for it to be economical.
[0006] Yet another potential method to enhance the recovery of
heavy crude oils is the Toe-To-Heel Injection (THAI) process
proposed by the University of Bath. THAI involves both vertical
wells and a pair of horizontal wells similar to that used in the
SAGD configuration, and uses combustion as the thermal source.
Thermal cracking of heavy oil in the porous media is realized, and
the high temperature in the mobile oil zone provides efficient
thermal sweeping of the lighter oil to the production well.
[0007] Even when they are recovered, heavy crude oils present
problems in refinement. Heavy and light crude oil processing will
give the same range of refined products but in very different
proportions and quantities. Heavy oils give much more vacuum
residues than lighter oils. These residues have an API between one
and five and very high sulfur and metals content, which makes
treatment difficult. Several processes exist to convert vacuum
residues. They are thermal, catalytic, chemical, or combinations of
these methods. Thermal processes include visbreaking,
aquathermolysis and coking.
[0008] Solvent deasphalting (SDA) is a proven process which
separates vacuum residues into low metal/carbon deasphalted oil and
a heavy pitch containing most of the contaminants, especially
metals. Various types of hydrotreating processes have been
developed as well. The principle is to lower the carbon to hydrogen
ratio by adding hydrogen, catalysis such as tetralin. The goal is
to desulfurize and remove nitrogen and heavy metals. These
processes may require temperature control, pressure control, and
some form of reactor technology such as fixed bed, ebullated bed,
or slurry reactor.
[0009] Recent concepts associate different processes to optimize
the heavy crude conversion. For example, the combination of
hydrotreating and solvent deasphalting in refineries or on site for
partial upgrading of heavy crude may be used.
[0010] Finally, the process of gasification for upgrading heavy oil
is used. It consists of conversion by partial oxidation of feed,
liquid, or solid into synthesis gas in which the major components
are hydrogen and carbon monoxide.
[0011] There is a need for an apparatus and method to enhance the
recovery of heavy crude oils that does not suffer from the
drawbacks associated with current methods. In particular, there is
a need for a method that does not use steam or water from external
sources, solvents that must be recovered, or combustion. Ideally,
such an apparatus and method would at the same time assist in the
in situ refinement of the heavy oil.
[0012] The present invention provides just such a method and
apparatus. It utilizes radiofrequency energy to combine enhanced
oil recovery with physical upgrading of the heavy oil.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention provides a system and method to apply
radiofrequency energy to in-situ heavy crude oil to heat the oil
and other materials in its vicinity. This system and method enhance
the recovery of the heavy crude oil. At the same time, it may be
used to upgrade the heavy crude oil in situ.
[0014] This system enhances the recovery of oil through a thermal
method. Heavy crude oils have high viscosities and pour points,
making them difficult to recover and transport. Heating the oil,
however, lowers the viscosity, pour point, and specific gravity of
the oil, rendering it easier to recover and handle. Thus, in the
present invention, directed radiofrequency radiation and absorption
are used to heat heavy oil and reduce its viscosity, thus enhancing
recovery. This dielectric heating also tends to generate fissures
and controlled fracture zones in the formation for enhanced
permeability and improved flow recovery of fluids and gases.
[0015] The system of the present invention is an in-situ
radiofrequency reactor (RFR) to apply radiofrequency energy to
heavy crude oil in situ. The RFR incorporates an in-situ
configuration of horizontal and vertical wells in a heavy crude oil
field. Using these wells, the RFR creates a subterranean reactor
for the optimum production and surface recovery of the heavy crude
oil. The RFR will provide an oil/hydrocarbon vapor front that will
optimize recovery of the oil.
[0016] In it simplest form, the RFR may consist of two wells in the
oil field, one a radiofrequency well and the second an oil/gas
producing well. At least a portion of both wells are horizontal in
the oil field, and the horizontal portion of the radiofrequency
well is above the horizontal portion of the oil/gas producing well.
A radiofrequency transmission line and antenna are placed in the
horizontal radiofrequency well and used to apply radiofrequency
energy to the oil, thereby heating it. The resulting reduction in
the viscosity of the oil and mild cracking of the oil causes the
oil to drain due to gravity. It is then recovered through the
horizontal oil/gas producing well. Naturally, any number of
radiofrequency and oil/gas producing wells can be used to create an
RFR for the recovery of heavy crude oils.
[0017] The invention also has the capability of further enhancing
recovery through the directed upgrading of the heavy oil in situ.
The horizontal radiofrequency well may be strongly
electromagnetically coupled to the horizontal oil/gas producing
well so that the temperature of the horizontal oil/gas producing
well may be precisely controlled, thereby allowing for upgrading of
the heavy oil in the producing well over a wide range of
temperatures. The oil/gas producing well may be embedded in a fixed
bed of material, such as a catalyst bed, selected to provide
upgrading of the crude oil draining from above. The upgrading can
be based on several different known technologies, such as
visbreaking, coking, aquathermolysis, or catalytic bed reactor
technology.
[0018] The present invention has several promising advantages over
present methods used to enhance recovery of heavy oil. In
particular, the RFR does not require the use of water from external
sources. This reduces expense and makes the recovery more
economical and efficient. Furthermore, the present invention does
not require the use of expensive solvents. Through the use of the
present invention, enhanced recovery of heavy crude oil can be
achieved more efficiently and cost-effectively.
[0019] Furthermore, in situ processing of crude oil has several
advantages over conventional oil surface upgrading technology.
First, in situ upgrading can be applied on a well to well basis, so
that large volumes of production needed for surface processes are
not required. Large, costly pressure vessels are not required since
the reservoir formation serves as a reactor vessel. It can be
applied in remote locations where a surface refinery would be
inappropriate. Some of the required gases and possibly water can be
generated in situ by the radiofrequency energy absorption. Finally,
full range whole crude oils are treated by RFR and not specific
boiling range fractions as is commonly done in refineries. This is
made possible by the ability of radiofrequency absorption to
provide precise temperature control throughout the reactor volume.
The proposed reactor provides large quantities of heat through
radiofrequency absorption close to the production well where the
catalyst bed is placed. No heat carrying fluids are necessary with
radiofrequency heating.
[0020] In one embodiment of the invention, an in situ
radiofrequency reactor for use in thermally recovering oil and
related materials may be provided. The reactor may comprise at
least one radiofrequency heating well in an area in which crude oil
exists in the ground, a radiofrequency antenna positioned within
each radiofrequency heating well in the vicinity of the crude oil,
a cable attached to each radiofrequency antenna to supply
radiofrequency energy to such radiofrequency antenna, a
radiofrequency generator attached to the cables to generate
radiofrequency energy to be supplied to each radiofrequency
antenna, and at least one production well in proximity to and below
the radiofrequency wells for the collection and recovery of crude
oil.
[0021] In another embodiment of the invention, an in situ
radiofrequency reactor for use in thermally recovering oil and
related materials and refining heavy crude oil in situ may be
provided. The reactor may comprise at least one radiofrequency
heating well in an area in which crude oil exists in the ground, a
radiofrequency antenna positioned within each radiofrequency
heating well in the vicinity of the crude oil, a cable attached to
each radiofrequency antenna to supply radiofrequency energy to such
radiofrequency antenna, a radiofrequency generator attached to the
cables to generate radiofrequency energy to be supplied to each
radiofrequency antenna, at least one production well in proximity
to and below the radiofrequency wells and coupled magnetically to
the radiofrequency wells for the collection and recovery of crude
oil, and at least one catalytic bed in which the production well is
embedded.
[0022] In yet another embodiment of the invention, a method for
recovering heavy crude oil is provided. The method comprises the
steps of positioning a radiofrequency antenna in a well in the
vicinity of heavy crude oil, generating radiofrequency energy,
applying the radiofrequency energy to the heavy crude oil with the
radiofrequency antenna to heat the oil, and recovering the heavy
crude oil through production well.
[0023] In one aspect, in general, a radiofrequency reactor for use
in thermally recovering oil and related materials. The
radiofrequency reactor includes a radiofrequency antenna configured
to be positioned within a well, where the well is provided within
an area in which crude oil exists in the ground. The radiofrequency
antenna includes a cylindrically-shaped radiating element for
radiating radiofrequency energy into the area in which crude oil
exists. The cylindrically-shaped radiating element is configured to
allow passage of fluids there through. The radiofrequency reactor
also includes a radiofrequency generator electrically coupled to
the radiofrequency antenna. The radiofrequency reactor is operable
to control the radiofrequency energy generated.
[0024] Aspects may include one or more of the following.
[0025] The cylindrically-shaped radiating element in the
radiofrequency reactor includes a plurality of apertures for
allowing passage of the fluids. In some examples, the plurality of
apertures have dimensions selected on the basis of the frequency of
the radiofrequency energy.
[0026] The radiofrequency reactor includes a coaxial cable for
coupling the radiofrequency antenna to the radiofrequency
generator.
[0027] The radiofrequency reactor includes a choke assembly
positioned between the radiofrequency antenna and radiofrequency
generator to maximize transmission of the radiofrequency energy to
the radiofrequency antenna. In some examples, the choke assembly
includes an inner conductive casing surrounded by a dielectric
portion, the assembly running at least one-quarter of a maximal
frequency to be emitted, and the inner casing is connected to a
cable for coupling the radiofrequency antenna to the radiofrequency
generator.
[0028] The radiofrequency reactor may be one of a plurality of
reactors. In such a situation, the radiofrequency generator of each
reactor is operable to control the radiofrequency energy generated
and is configured to work in conjunction with the radiofrequency
generators of the plurality of reactors.
[0029] The radiofrequency generator operable to control the
radiofrequency energy generated is configured to control the phase
of the radiofrequency energy emitted.
[0030] In another aspect, in general, a method of retrofitting an
oil well for extracting crude oil. The method includes electrically
coupling a radiofrequency generator to a radiofrequency antenna,
where the radiofrequency antenna includes a cylindrically-shaped
radiating element for radiating radiofrequency energy into the
crude oil. The method also includes controlling the radiofrequency
generator to provide radiofrequency energy to the radiofrequency
antenna.
[0031] Aspects may include one or more of the following.
[0032] Positioning the radiofrequency generator proximally to the
well surface and electrically coupling the radiofrequency generator
to the cylindrically-shaped radiating element via a coaxial
cable.
[0033] Connecting a choke assembly between the radiofrequency
generator and the cylindrically-shaped radiating element.
[0034] Controlling the radiofrequency generator to provide
radiofrequency energy to the radiofrequency antenna, including
controlling the phasing of the radiofrequency energy emitted.
[0035] While multiple embodiments are disclosed, still other
embodiments of the present invention will become apparent to those
skilled in the art from the following detailed description, which
shows and describes illustrative embodiments of the invention. As
will be realized, the invention is capable of modifications in
various obvious aspects, all without departing from the spirit and
scope of the present invention. Accordingly, the drawings and
detailed description are to be regarded as illustrative in nature
and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a perspective view of a basic in situ
radiofrequency reactor.
[0037] FIG. 2 is a perspective view of an alternative arrangement
of an in situ radiofrequency reactor.
[0038] FIG. 3 is a top view of an arrangement for an in situ
radiofrequency reactor for use in large oil fields.
[0039] FIG. 4 is a perspective view of a single borehole radiation
type applicator that may be used in the radiofrequency reactor of
the present invention.
[0040] FIG. 5 is a diagram of a prior art steam assisted gravity
drainage (SAGD) system.
[0041] FIG. 6 is a diagram of a well retrofitted as an in situ
radiofrequency reactor.
[0042] FIG. 7 is a diagram of a slotted liner protruding from a
well shaft.
DETAILED DESCRIPTION
[0043] A variety of different arrangements of wells and antennae
may be employed to apply radiofrequency energy to heavy crude oil
in situ, thereby enhancing oil recovery and achieving in situ
upgrading of the oil. The proper structure and arrangement for any
particular application depends on a variety of factors, including
size of field, depth, uniformity, and nature and amount of water
and gases in the field.
[0044] FIG. 1 is a perspective view of a basic in situ
radiofrequency reactor. Heavy oil is present in oil field 10.
Oil/gas production well 20 is drilled into the oil field for
recovery of heavy oil and other materials. At least a portion of
oil/gas production well 20 is drilled horizontally through the oil
field. Horizontal oil/gas production well 21 is positioned to
receive oil and other gas that are moved or generated by the action
of the radiofrequency reactor. A second well, radiofrequency well
30, is drilled into the oil field in proximity to oil/gas
production well 20. At least a portion of radiofrequency well 30 is
drilled horizontally through the oil field in proximity to and
above horizontal oil/gas production well 21. Horizontal
radiofrequency well 31 is used to apply radiofrequency energy to
the surrounding heavy crude oil field, thereby heating the oil and
reducing its viscosity. Due to gravity, the reduced heated heavy
crude oil drains, where it may be captured by and pumped out
through oil/gas production well 20 to storage or processing
equipment.
[0045] Radiofrequency energy is generated by a radiofrequency
generator. It is transmitted via radiofrequency transmission line
40 through radiofrequency well 30 and horizontal radiofrequency
well 31 to radiofrequency antenna 41. Radiofrequency antenna 41
applies radiofrequency energy to the surrounding heavy crude oil,
thereby heating it and reducing its viscosity so that it may be
collected by and recovered through oil/gas production well 20. The
oil/gas production well 20 may also act as a parasitic antenna to
redirect radiation in an upward direction toward the formation to
be heated by the radiofrequency energy, thereby increasing
efficiency.
[0046] For purposes of in situ processing and upgrading of the
heavy crude oil, horizontal oil/gas production well 21 may be
embedded in catalytic bed 50. Horizontal radiofrequency well 31 may
be strongly electromagnetically coupled to horizontal oil/gas
producing well 21 so that the temperature of horizontal oil/gas
producing well 21 may be precisely controlled, thereby allowing for
upgrading of the heavy oil in horizontal oil/gas production well 21
over a wide range of temperatures. The upgrading can be based on
several different known technologies, such as visbreaking, coking,
aquathermolysis, or catalytic bed reactor technology.
[0047] Radiofrequency antennae may be placed in an oil field in
numerous configurations to maximize oil recovery and efficiency.
FIG. 2 shows a perspective view of an alternative arrangement of an
in situ radiofrequency reactor. Radiofrequency antennae 41 may be
placed in proximity to one another in oil field 10. Radiofrequency
energy is supplied to the antennae 41 by a radiofrequency generator
and then applied to the oil field 10. The resulting heating reduces
the viscosity of the oil, which drains due to gravity. Horizontal
oil/gas production well 21 is positioned below the antennae 41 to
collect and recover the heated oil.
[0048] As with the RFR in FIG. 1, this arrangement may also be used
to process the heavy oil in situ. A horizontal radiofrequency well
31 with horizontal radiofrequency antenna 42 may be placed in
proximity to horizontal oil/gas producing well 21 below antennae 41
to control the temperature of the oil. Horizontal oil/gas
production well 21 may be embedded in catalytic bed reactor 50. The
oil may thereby be upgraded in situ.
[0049] FIG. 3 shows a top view of another arrangement for an in
situ radiofrequency reactor for use in large oil fields. In this
radial configuration, one central and vertical radiofrequency
heating well 32 with radiofrequency antenna 41 is used for larger
volumes of oil. Radiofrequency antenna 41 applies radiofrequency
energy to area 11, thereby heating the oil in that area. The heated
oil drains to horizontal oil/gas production wells 21 for collection
and recovery. Parallel horizontal radiofrequency wells 31 may also
be used to heat the oil. In addition, radiofrequency antennae 43
may be placed in vertical radiofrequency wells 33 to assist with in
situ upgrading of the heavy crude oil.
[0050] The radiofrequency antennae used in the RFR system of the
present invention may be any of those known in the art. FIG. 4
shows a perspective view of a radiofrequency applicator that may be
used with the RFR of the invention. Applicator system 45 is
positioned within radiofrequency well 30. Applicator system 45 is
then used to apply electromagnetic energy to heavy crude oil in the
vicinity of radiofrequency well 30.
[0051] Applicator structure 46 is a transmission line retort.
Radiofrequency energy is supplied to applicator 46 by an RF
generator (not shown). The radiofrequency generator is connected to
applicator 46 via radiofrequency transmission line 40. The
radiofrequency transmission line 40 may or may not be supported by
ceramic beads, which are desirable at higher temperatures. By this
means, the radiofrequency generator supplies radiofrequency energy
to applicator 46, which in turn applies radiofrequency energy to
the target volume of oil.
[0052] Although one specific examples of an applicator structure is
given, it is understood that other arrangements known in the art
could be used as well. Uniform heating may be achieved using
antenna array techniques, such as those disclosed in U.S. Pat. No.
5,065,819.
[0053] The present invention also has application in oil shale
fields, such as those present in the Western United States. Large
oil molecules that exist in such oil shale have been heated in a
series of experiments to evaluate the dielectric frequency response
with temperature. The response at low temperatures is always
dictated by the connate water until this water is removed as a
vapor. Following the water vapor state, the minerals control the
degree of energy absorption until temperatures of about 300-350
degrees centigrade are reached. In this temperature range, the
radiofrequency energy begins to be preferentially absorbed by the
heavy oil. The onset of this selective absorption is rapid and
requires power control to insure that excessive temperatures with
attendant coking do not occur.
[0054] Because of the high temperature selective energy absorption
capability of heavy oil, it is therefore possible to very carefully
control the bulk temperature of crude oil heated by radiofrequency
energy. The energy requirement is minimized once the connate water
is removed by steaming. It takes much less energy to reach mild
cracking temperatures with radiofrequency energy than any other
thermal means.
[0055] Kasevich has published a molecular theory that relates to
the specific heating of heavy of oil molecules. He found that by
comparing cable insulating oils with kerogen (oil) from oil shale,
a statistical distribution of relaxation times in the kerogen
dielectric gave the best theoretical description of how
radiofrequency energy is absorbed in oil through dielectric
properties. With higher temperatures and lowering of potential
energy barriers within the molecular complex a rapid rise in
selective energy absorption occurs.
[0056] In use, a user of an embodiment of the present invention
would drill oil/gas production wells and radiofrequency wells into
a heavy crude oil field. At least a portion of the wells would be
horizontal. The radiofrequency wells would be placed in proximity
to and above the oil/gas production wells. The user would install a
radiofrequency antenna in each radiofrequency well and supply such
antennae with radiofrequency energy from a radiofrequency generator
via a radiofrequency transmission cable. The user would then apply
radiofrequency energy using the radiofrequency generator to the
antenna, thereby applying the radiofrequency energy to the heavy
crude oil in situ. The radiofrequency energy would be controlled to
minimize coking and achieve the desired cracking and upgrading of
the heavy crude oil. The resulting products would then be recovered
via the oil/gas production well and transferred to a storage or
processing facility.
[0057] Referring again to FIG. 4, the applicator structure 46 is a
vertical monopole antenna within a non-metallic production pipe
(shown as a radiofrequency well 30). The production pipe extension
below the applicator or antenna may be used to enhance the
radiation efficiency by adjusting the length of the pipe. The pipe
may extend into or below the subterranean oil or gas.
[0058] As described in the above background section, steam assisted
gravity drainage (SAGD), is an existing commercial process for
heavy oil recovery, used especially in high permeability reservoirs
such as those encountered in the oil sands of Western Canada.
Referring to FIG. 5, in the SAGD process, two parallel horizontal
oil wells 520 & 550 are drilled in the formation, one above the
other (in some examples, roughly 10 meters apart). The upper well
acts as a steam injector 520 and typically includes a slotted liner
522 (in some examples, roughly 300 meters long) for allowing steam
to be released through the slots 530. The steam increases the
temperature of the crude oil in the oil sand formation 512,
reducing the crude oil's viscosity and allowing it to be collected
by gravity drainage via the lower well, referred to as an oil
producer 550. The slotted liner 522 is typically made of conductive
materials.
[0059] Referring to FIG. 6, in some embodiments, the SAGD
configuration is retrofitted to use one or both wells (or portions
thereof, e.g., the liners) as an antenna for emitting RF energy
into the oil sand formation. The RF energy increases the
temperature of the crude oil, reducing its viscosity and allowing
it to be collected. In some embodiments the oil is collected using
a pipe (not shown) within the same well as the well 600 configured
to host an antenna.
[0060] A coaxial cable 630 connects a power source (not shown), for
example, a radiofrequency generator stationed on the surface, to
the slotted liner 622. The coaxial cable 630 has a central
conductor 632 surrounded by a dielectric insulating portion and an
outer conductive shield 634. In some embodiments, the outer
conductor 634 is also wrapped in an external insulating layer.
[0061] At the distal end of the well, the coaxial cable's central
conductor 632 is electrically connected to the well's slotted liner
622. In some embodiments, the connection to the liner 622 is
achieved using a metal contact ring 660 to which the central
conductor 632 is electrically connected 664 (e.g., welded). The
contact ring 660 is mated with the liner 622.
[0062] In some embodiments, an insulating section 650 is used, for
example, to separate the slotted liner 622 from the well wall 620.
The insulating section 650 is a hollow cylinder that allows the
coaxial cable 630 and any other cables or pipes (e.g., an oil
collection pipe) to pass through it. In some examples, the
insulating section 650 is ceramic.
[0063] As shown if FIG. 6, the well 600 is supported in the earth
616 by a cement casing 614. The cement 614 is susceptible to
cracking if subjected to excessive heat. In such embodiments, it
may be desirable to restrict the level of RF energy returning up
the well 600, for example, to reduce the risk of the cement 614
cracking. Therefore, a high impedance block is created.
[0064] In the embodiment shown in FIG. 6, the outer conductor 634
of the coaxial cable 630 is electrically connected 648 to a
quarter-wave choke assembly 640. The optimal length of the choke
assembly is an odd multiple of quarter-wavelengths (1/4, 3/4, 5/4,
etc.). That is, the choke assembly 640 extends back from the
insulator 650 at least one quarter of the maximum wavelength for
the energy to be emitted from the antenna. The choke assembly 640
may extend further back, in some examples, extending all of the way
back to the surface.
[0065] The quarter-wave choke assembly 640 includes an inner
conductor 642, which is separated from either the well wall 620 or
an outer assembly casing 644 by either air or a dielectric layer
646. The outer conductor 634 of the coaxial cable 630 is
electrically connected 648 to the inner conductor 642 of the choke
assembly 640. The inner conductor 642 is shorted 654 to the inner
side of the well wall 620 at the proximal end of the choke assembly
640.
[0066] The quarter-wave choke assembly 640 creates a high impedance
block restricting the flow of energy back up the well 600.
Alternatively, in some embodiments, the outer conductor 634 is
electrically connected directly to the inside of the well wall
620.
[0067] Referring again to FIG. 5, in certain embodiments, multiple
wells (e.g., both the steam injector 520 and the oil producer 550)
are retrofitted as RF antennas. In such embodiments, the multiple
antennas are powered in a manner to boost the RF energy, for
example, by emitting energy in phase. In other embodiments, the
phase of the energy emitted by each of the multiple antennas can be
tuned to control the energy levels within the oil sand formation by
controlling the antennas to emit out of phase.
[0068] In certain applications, the slots in the slotted liner are
sized in a manner to increase the efficacy of subsequent RF
retrofit. Referring to FIG. 7, in some embodiments, a well 700 is
configured with two slotted liners--an inner liner 710 and an outer
liner 720. Each liner includes slots 730. At least one liner, e.g.,
the inner liner 710, is configured to be adjusted, acting as a
telescoping sleeve. By telescoping the liner, the size of the slots
730 are adjusted. The liner overlap 740 therefore creates variably
sized slots. Using this approach, the slots in the slotted liner
are dynamically sized as needed.
[0069] In some embodiments, the presence of the RF retrofit does
not preclude the contemporary use of steam or other oil recovery
methods. For example, the RF energy is used to initiate the process
of oil recovery by alternative means.
[0070] Although the present invention has been described with
reference to preferred embodiments, persons skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
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